Sign in after the transition

If your Google Account through your work, school, or other group is being transitioned while you're already signed in to the account, then you will be automatically signed out when the transition is complete. Thus, you will need to sign back in to access your transitioned account. After your account completes the transition, there are two ways you can sign in going forward:

You can use your work, school, or other group's original sign-in page to sign in as you had been doing, prior to the transition. For example, visiting https://mail.google.com/a/domain.com

You can use the regular sign-in pages for Google products, such as www.gmail.com or sites.google.com. If you choose to sign in using these sign-in pages, make sure to sign in with your full email address. This means you need to enter 'username@my-domain.com' in the 'Email:' field.